1. Technical Field
The present invention relates to a computer power supply system and, more particularly, to a computer power supply system which includes a smart battery pack and a variable output battery charger system which enables optimal charging of the battery pack during all operating conditions while allowing the power supply to be utilized with battery packs having different charging characteristics.
2. Description of the Prior Art
Power supply systems are generally known in the art. Such systems are utilized in a variety of applications to provide electrical power to portable devices, such as portable personal computers. Such power supply systems normally include a battery pack and a battery charger system. The battery charger systems are used to charge the battery packs and to enable a computer or other portable device to be operated from a source of AC electrical power. The battery pack normally provides several hours of portable operation before requiring recharging.
Various types of batteries are known. More particularly, nickel cadmium (NiCd) and nickel-metal hydride (NiMH) batteries have been known to be used in applications for portable personal computers. Such batteries generally provide a few hours of operation before requiring recharging. The charging characteristics of such batteries enable such batteries to be recharged by relatively simple battery chargers having two fixed modes of operation: a trickle charge mode and a fast charge mode. In the trickle charge mode, the battery charger provides a relatively low level constant current (e.g., 100 milliamperes) to the battery over a relatively long time, for example ten to twelve hours. In a fast charge mode, a relatively higher current level (e.g., 2 amperes) is applied to the battery over a relatively shorter period of time, for example one to three hours. In order to prevent damage to the batteries, the charge level of the batteries is continuously sensed. When the battery reaches its maximum charge level, the battery charging is terminated in order to prevent overheating and damage of the batteries.
Various systems are known for implementing a battery pack and battery charger in a portable personal computer. The degree of integration of the power supply system with the computer system varies. In one known system, a system control processor (SCP) is used to measure the charge level of the battery as well as the operational status (e.g., on-off) of the computer. In particular, signals representative of the battery voltage and temperature as well as the on-off status of the computer system are applied to the SCP which, in turn, provides a logic level signal to control the battery charger. Depending on the level of charge of the battery and the on-off status of the computer system, the SCP enables either a fast charge for a relatively short time or a trickle charge for a relatively longer time in order to charge the battery.
There are several problems associated with such a system. First, any changes to a battery technology having different charging characteristics or changes in battery capacity require some redesign of the computer system and redesign of the battery charger. Second, utilizing the SCP to monitor the charge level of the battery pack and the operating status of the computer system places an additional burden on the SCP; normally used to provide a communication between the keyboard and the central processing unit.
In an alternate known embodiment, the battery charger and battery pack have known to be provided as independent modules, disposed in separate enclosures relative to the computer system. In such an application, either one or both of the modules are adapted to be connected to the computer system at one time. This enables the computer system to be operated from either the battery pack or the battery charger. Such an application also allows the battery pack and battery charger module to be connected to the computer system at the same time, thus enabling batteries to be charged while the battery charger is operating the computer system. Moreover, the system also enables the battery charger to be used to charge the battery pack separately from the computer system.
In order to alleviate the burden on the SCP, a dedicated microprocessor is used in the alternate embodiment to monitor the charge level of the battery and the operating status of the computer system in order to control a two-level battery charging system as discussed above. The dedicated microprocessor is located in the housing with the battery charger. However, even though such a dedicated microprocessor alleviates the burden on the SCP, any change in the battery technology to one having different charging characteristics or changes in the battery capacity still requires a design change of the battery charger, thus making such changes of battery technology or capacity relatively costly to a computer manufacturer.
In another known alternate embodiment, in an attempt to improve the modularity of the system, a dedicated microprocessor is disposed in the battery pack to enable the battery pack to be more of a stand-alone subsystem. Such a system provides the ability to upgrade to a different type of battery pack having similar charge/discharge characteristics.
However, the above mentioned system as well as the other systems discussed above utilize battery chargers that provide fixed level current charging to the battery pack. More particularly, whether controlled from the SCP or from a dedicated processor, the battery chargers discussed above are known to operate in two fixed current modes; namely, a fast charge mode and a trickle charge mode. Although such charging characteristics are suitable for nickel cadmium batteries and other types of batteries, such charging characteristics may not be suitable for new battery technologies which have recently become available that provide for higher energy density. Such new battery technologies may require different charging characteristics which could not be provided by the known battery charging systems discussed above. For example, new battery technologies may be less tolerant of continuous overcharge in order to maintain the battery at full capacity in contradistinction to nickel cadmium batteries. In addition, the fixed two-level charge characteristics of known battery chargers may not be suitable because of the capacity rating (the fast charge current may be too high or too low). With such new battery technologies, the battery charging circuit has to be redesigned for each different battery technology used.
Another problem with such known power supply systems is the inability of such systems to efficiently utilize the capacity of the battery charger. This inability is based on the failure of such known systems to detect the current load demand placed on the AC power supply battery charger by the computer system. In such systems, a worst-case design approach is known to be used which inhibits fast charging of the battery pack while the computer system is operational in order to avoid exceeding the capacity of the battery charger. In particular, in order to keep the cost and the weight of the system down, the battery charger capacity is known to be sized based on an estimate of the maximum load demand of the computer system. However, it is known that during the majority of time, the computer system is not operating at maximum load. Thus, with known power supply systems, fast charging of the battery pack is inhibited during the majority of time, thereby utilizing only a fraction of the available capacity of the battery charger. Thus, during such periods when the computer system is not operating at maximum load, a surplus or residual capacity of the battery charger is idle instead of being used to charge the battery pack at other than a trickle charge rate.